Interfacing Programs for 8085

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INTERFACING PROGRAMS FOR 8085

PROGRAM TO INTERFACE 16 LED’S TO 8255 PORTS AND DISPLAY THEM AS PER THE SPECIFIED PATTERN.

0 1 2 3 4 5 6 7

LA 1 0 1 0 1 0 1 0 AAH

LB 0 1 0 1 0 1 0 1 55H

THE PROGRAM BELOW IS USED TO DISPLAY PATTERN AS ABOVE AND CERTAIN SEQUENCES.

8000 MVI A 80 3E ;

8001 80 ;

8002 OUT CW D3 ;

8003 43 ;

8004 MVI A AA 3E ;

8005 AA ;

8006 OUT PA D3 ;

8007 40 ;

8008 CALL DLY CD ;

8009 00 ;

800A 85 ;

800B CMA 2F ;

800C OUT PB D3 ;

800D 41 ;

800E CALL DLY CD ;

800F 00 ;

8010 85 ;

8011 MVI C 08 0E ;

8012 08 ;

8013 RRC 0F ;

8014 OUT PB D3 ;

8015 41 ;

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8016 CALL DLY CD ;

8017 00 ;

8018 85 ;

8019 DCR C 0D ;

801A JNZ 8013 C2 ;

801B 13 ;

801C 80 ;

801D MVI A AA 3E ;

801E AA ;

801F MVI C 08 0E ;

8020 08 ;

8021 RRC 0F ;

8022 OUT PA D3 ;

8023 40 ;

8024 CALL DLY CD ;

8025 00 ;

8026 85 ;

8027 DCR C 0D ;

8028 JNZ 8021 C2 ;

8029 21 ;

802A 80 ;

802B JMP 8004 C3 ;

802C 04 ;

802D 80 ;

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INTERFACING 8085 TO DAC

A)TO GENERATE SQUARE WAVEFORM

TO GENERATE SQUARE WAVEFORM USING DAC JUST WE

HAVE TO SEND TWO DIFFERENT VALUES TO DAC THAT IS

FOR LOW LEVEL AND HIGH LEVEL AND A PROPER

DELAY.THE DELAY DEFINES THE FREQUENCY OF SQUARE

WAVE.THE PROGRAM IS AS FOLLOWS :

0000 LXI SP8500 31 ;

0001 00 ;

0002 85 ;

0003 MVI A 80 3E ;

0004 80 ;

0005 OUT CW D3 ;

0006 40 ;

0007 MVI A 00 3E ;

0008 00 ;

0009 OUT PA D3 ;

000A 41 ;

000B CALL DLY CD ;

000C 00 ;

000D 85 ;

000E CMA 2F ;

000F JMP 0009 C3 ;

0010 09 ;

0011 00 ;

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B)

PROGRAM TO GENERATE TRIANGULAR WAVE USING DAC

0000 LXI SP8500 31 ;

0001 00 ;

0002 85 ;

0003 MVI A 80 3E ;

0004 80 ;

0005 OUT CW D3 ;

0006 40 ;

0007 MVI A 00 3E ;

0008 00 ;

0009 OUT PA D3 ;

000A 41 ;

000B CALL DLY CD ;

000C 00 ;

000D 85 ;

000E INR A 3C ;

000F CPI FF FE ;

0010 FF ;

0011 JNZ 0009 C2 ;

0012 09 ;

0013

00 ;

0014 OUT PA D3 ;

0015 41 ;

0016 DCR A 3D ;

0017 CALL DLY CD ;

0018 00 ;

0019 85 ;

001A JNZ 8014 C2 ;

001B 14 ;

001C

00 ;

001D JMP 8009 C3 ;

001E 09 ;

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001F

00 ;

C)PROGRAM TO GENERATE SAWTOOTH WAVEFORM USING

DAC

0000 LXI SP8500 31 ;

0001 00 ;

0002 85 ;

0003 MVI A 80 3E ;

0004 80 ;

0005 OUT CW D3 ;

0006 40 ;

0007 MVI A 00 3E ;

0008 00 ;

0009 OUT PA D3 ;

000A 41 ;

000B CALL DLY CD ;

000C 00 ;

000D 85 ;

000E INR A 3C ;

000F JMP 0009 C3 ;

0010 09 ;

0011 00 ;

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D)PROGRAM TO GENERATE STAIRCASE WAVE USING DAC

TO GENERATE STAIRCASE WAVEFORM IT IS REQUIRED

TO CALUCLATE THE STEP SIZE. THE STEPSIZE IS

CALUCLATED AS FOLLOWS :

IF NUMBER OF STEPS = N

THEN STEP SIZE = (MAX. AMPLITUDE / N)

THE MAXIMMUM VALUE OF AN 8-BIT SYSTEM IS FFH.

AND THE MAXIMUM AMPLITUDE IS 5V. SO FOR 5 STEPS

THE STEPSIZE IS

FF/N = 255/5 = 51 = 33H

0000 MVI A 80 3E ;

0001 80 ;

0002 OUT CW D3 ;

0003 40 ;

0004 MVI A 00 3E ;

0005 00 ;

0006 OUT PA D3 ;

0007 41 ;

0008 CALL DLY CD ;

0009 00 ;

000A 85 ;

000B ADI 33 C6 ;

000C

33 ;

000D

JNC 0006 D2 ;

000E 06 ;

000F 00 ;

0010 JMP 0004 C3 ;

0011 04 ;

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0012 00 ;

E)

PROGRAM TO GENERATE EXPONENTIAL WAVEFORM USING DAC.

0000 LXI SP8500 31 ;

0001 00 ;

0002 85 ;

0003 MVI A 80 3E ;

0004 80 ;

0005 OUT CW D3 ;

0006 40 ;

0007 MVI A 00 3E ;

0008 00 ;

0009 STC 37 ;

000A RAL 17 ;

000B OUT PA D3 ;

000C 41 ;

000D CALL DLY CD ;

000E 00 ;

000F 85 ;

0010 CPI 40 FE ;

0011 40 ;

0012 JNZ 000A C2 ;

0013 0A ;

0014

00 ;

0015 RAR 1F ;

0016 OUT PA D3 ;

0017 41 ;

0018 CALL DLY CD ;

0019 00 ;

001A 85 ;

001B CPI 01 FE ;

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001C 01 ;

001D JNZ 0015 C2 ;

001E 15 ;

001F 00 ;

0020 JMP 000A C3 ;

0021 0A ;

0022 00 ;

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F)

PROGRAM TO GENERRATE SINUSOIDAL WAVE USING DAC.

TO GENERATE SINUSOIDAL WAVEFORM WE USE LOOKUP TABLE METHOD.

LET Vθ = VPSINθ + VO IF WE SELECT THE AVERRAGE

VALUE OF THE SINE WAVE (THAT IS θ = 0O_{) AT THE MIDDLE}

OF THE AVAILABLE RANGE THE WAVEFORM CAN BE OF MAXIMUM POSSIBLE AMPLITUDE. THE FULL SWING IS LIMITED TO FFH IN AN 8-BIT SYSTEM. IF AVERAGE LEVEL V0IS SELECTED TO BE 80H THE VP (PEAK EXCURSION) CAN

BE FFH – 80H = 7FH. THUS THE WAVEFORM WILL TAKE FFH AT ITS POSITIVE PEAK(AT 90O_{)AND 01H(80H – 7FH) AT ITS}

NEGATIVE PEAK(AT 270O_{). PUTTING THE VALUES IN ABOVE}

EQUATION,

Vθ = 7FH SINθ + 80H

IF WE CALUCLATE SAMPLES WITH 5O_{INTERVALS V} θ

WILL TAKE VALUES AS FOLLOWS :

8000 MVI A 80 3E ;

8001 80 ;

8002 OUT CW D3 ;

8003 40 ;

8004 LXI H 8500 21 ;

8005 00 ;

8006 85 ;

8007 MVI C 72 0E ;

8008 72 ;

8009 MOV A M 7E ;

800A OUT PA D3 ;

800B 41 ;

800C CALL DLY CD ;

800D 00 ;

800E 85 ;

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800F INX H 23 ;

8010 DCR C 0D ;

8011 JNZ 8009 C2 ;

8012 09 ;

8013 80 ;

8014 JMP 8004 C3 ;

8015 04 ;

8016 80 ;

Θ(DEG)

V

θ

Θ(DEG)

V

θ

Θ(DEG)

V

θ

Θ(DEG)

V

θ

5 8BH

95 FFH

185 75H

275 01H

10 96H

100 FDH

190 6AH

280 03H

15 A1H

105 FAH

195 5FH

285 05H

20 ABH

110 F7H

200 55H

290 09H

25 B6H

115 F3H

205 1AH

295 0DH

30 C0H

120 EEH

210 41H

300 12H

35 C9H

125 E8H

215 37H

305 18H

40 D2H

130 E1H

220 2EH

310 1FH

45 DAH

135 DAH

225 26H

315 26H

50 E1H

140 D2H

230 1FH

320 2EH

55 E8H

145 C9H

235 18H

325 37H

60 EEH

150 C0H

240 12H

330 41H

65 F3H

155 B6H

245 0DH

335 4AH

70 F7H

160 ABH

250 09H

340 55H

75 FAH

165 A1H

255 05H

345 5FH

80 FDH

170 96H

260 03H

350 6AH

85 FFH

175 8BH

265 01H

355 75H

90 FFH

180 80H

270 01H

360 80H

THE SAMPLED VALUES ARE KEPT IN THE MEMORY

STARTING FROM 8500 AND CALLED ONE BY ONE TO

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OBTAIN A SINUSOIDAL WAVEFORM THE FREQUENCY OF

SINUSOIDAL WAVEFORM DEPENDS ON THE DELAY

CALUCLATION.

8255 – PROGRAMMABLE PERIPHERAL INTERFACE

D7

D6

D5

D4

D3

D2

D1

D0

PORT C – PC3 – PC0 1 = INPUT 0 = OUTPUT PORT B – PB7 – PB0 1 = INPUT 0 = OUTPUT MODE 0 – MODE 0 1 – MODE 1

1 – I/O MODE

0 – BSR MODE

PORT C – PC7 – PC4 1 = INPUT 0 = OUTPUT

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PORT A – PA7 – PA0 1 – INPUT 0 – OUTPUT MODE 00 – MODE 0 01 – MODE 1 1X – MODE

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WE KNOW THAT 8085 MICROPROCESSOR DOES NOT CONTAIN ANY PORTS TO IT TO INTERFACE PERIPHERAL DEVICES HENCE IT REQUIRES AN ADDITIONAL CHIP SO AS TO INTERFACE PERIPHERAL DEVICES FOR THIS TO BE

ACHIEVED WE USE A PROGRAMMABLE PERIPERAL INTERFACE 8255 IC.

THIS IC CONSISTS OF 3 PORTS NAMELY PORT A, PORT B, PORT C EACH OF WIDTH 8-BIT . HERE IN THIS CHIP TWO PORTS(PORT A AND PORT B) WORK AS 8-BIT PORTS BUT PORT C CAN WORK AS 8-BIT PORT OR AS TWO 4-BIT

PORTS.

HERE WE CAN CONCLUDE THAT OUR 8255 PROVIDES US THE TOTAL OF 24 LINES (3 PORTS) WHICH CAN BE USED EITHER AS INPUT OR OUTPUT PORTS.

BUT TO DEFINE ALL THIS PORTS AND MODES WE REQUIRE A WORD TO DEFINE ALL THIS WHETHER TO SELECT PORTS AS INPUT OR OUTPUT OTHERWISE FOR MODE SELECTION ETC., THIS WORD IS KNOWN AS CONTROL WORD.

THE 8085 CAN OPERATE IN THREE MODES OF OPERRATION

1. SIMPLE I/O MODE. 2. STROBED I/O MODE.

3. BIDIRECTIONAL DATA TRANSFER.

DURING INTERFACING WE USE SIMPLE I/O MODE FOR INTERFACING DAC’S, ADC’S, LED DISPLAYS ETC.,

STEPS TO INTERFACE EXTERNAL DEVICES WITH 8255 1. WRITE THE PROPER CONTROL WORD TO CONTROL

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2. IDENTIFY THE ADDRESSES OF THE PORTS (PORT A, PORT B, PORT C)

FROM THE MANUAL.

3. THE ADDRESSES FOR THE PORTS AND CONTROL

WORD REGISTER FOR THE KIT WE ARE USING ARE AS FOLLOWS :

CONTROL WORD -

PORT A

-PORT B

-PORT C -

BY USING THIS ADDRESSES WE CAN EITHER ACCEPT DATA AS INPUT OR WE CAN SEND DATA OUTPUT TO

CONTROL THE DEVICE.

THE LAST STEP IS TO PREPARE THE ALGORITHM AND WRITE THE PROGRAM AS PER THE REQUIREMENT.

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INTERFACING ADC TO 8085

TO INTERFACE ADC TO MICROPROCESSOR WE REQUIRE TO FOLLOW THE FOLLOWING STEPS:

 The analog part of the circuit consists of a high input impedance buffer a1, precision integrator a2 and a voltage comparator.

 The converter first integrates the analog input signal

va for a fixed duration of 2n clock periods.

 Then it integrates an internal reference voltage v_rof

opposite polarity until the integrator output is zero.

 The number n of clock cycles required to return the

integrator to zero is proportional to the value of va

averaged over the integration period.

 Hence, n represents the desired output code. The operation of the circuit is as follows :

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 Before the start command arrives, the switch sw1 is

connected to ground and sw2 is closed. Any offset voltage present in the a1, a2, comparator loop after integration, appears across the capacitor caz till the

threshold of the comparator is achieved.

 The capacitor caz thus provides automatic

compensation for the input offset voltage of all the three amplifiers.

 When sw2 opens, c_az acts as a memory to hold the

voltage required to keep the offset nulled.

 At the arrival of start command at t=t1 , the control

logic opens sw2 and connects sw1 to va and enables

the counter starting from zero.

 The circuit uses an n-stage ripple counter and

therefore the counter resets to zero after counting 2n

pulses.

 The analog voltage v_a is integrated for a fixed number

2n_{counts of clock pulses after which the counter}

resets to zero.

 If the clock period is t, the integration takes place for

a time t1 = 2n x t and the output is ramp going

downwards as in fig 2.

 The counter resets itself to zero at the end of the

interval t1 and the switch sw1 is connected to the

reference voltage (-vr). The output voltage vo will

now have a positive slope. As long as vo is negative ,

the output of the comparator is positive and control logic allows the clock pulse to be counted. However, when vo becomes just zero at time t=t3, the control

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logic issues an end of conversion(eoc) command and no further clock pulses enter the counter.

 It can be shown that the reading of the counter at t_s

is proportional to the analog input voltage va

In fig 2,

t1 = t2 – t1 = (2n counts / clock rate)

And t3 – t2 = (digital count n / clock rate)

For an integrator,

δv0 = (-1/rc)v(δt)

The voltage vo will be equal to v1 at the instant t2 and

can be written as

v1 = (-1/rc ) va(t2 – t1)

So, va (t2 – t1) = vr (t3 –t2)

Putting, the values of (t2 – t1) = 2n and (t3 – t2) = n, we

get,

va = (vr) (n/2n).

The main disadvantage of the dual slope ADC is long conversion time.

Program to Interface ADC to 8085 Microprocessor :

8000 MVI A 82 3E ;

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8001 82 ;

8002 OUT 43 D3 ;

8003 43 ;

8004 MVI A 02 3E ;

8005 02 ;

8006 OUT 40 D3 ;

8007 40 ;

8008 NOP 00 ;

8009 NOP 00 ;

800A NOP 00 ;

800B NOP 00 ;

800C NOP 00 ;

800D NOP 00 ;

800E MVI A 01 3E ;

800F 01 ;

8010 OUT 40 D3 ;

8011 40 ;

8012 LXI H 02C0 21 ;

8013 C0 ;

8014 02 ;

8015 DCX H 2B ;

8016 MOV A H 7C ;

8017 ORA L B5 ;

8018 JNZ 8015 C2 ;

8019 15 ;

801A 80 ;

801B MVI A 04 3E ;

801C 04 ;

801D OUT 40 D3 ;

801E 40 ;

801F MVI B 00 06 ;

8020 00 ;

8021 INR B 04 ;

8022 IN 41 DB ;

8023 41 ;

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8024 ANI 01 E6 ;

8025 01 ;

8026 JNZ 8021 C2 ;

8027 21 ;

8028 80 ;

8029 MVI A 02 3E ;

802A 02 ;

802B OUT 40 D3 ;

802C 40 ;

802D MOV A B 78 ;

802E STA 8501 32 ;

802F 01 ;

8030 85 ;

8031 HLT 76 ;

Integrator o/p voltage Vo

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Fig :- 2 :- integrated o/p waveform of dual slope ADC AUTOZER t2 t3 t1 T1 = 2n T N-Cycles Time T V1 Integrate Va Integrate (-VR)

Control

START N – STAGE d 0 d

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INTERFACING STEPPER MOTOR TO 8085 :

MOTOR ELECTRICAL BASICS

A step motor is a constant output power transducer, where power is defined as torque multiplied by speed. This means motor torque is the inverse of motor speed. To help understand why a step motor’s power is independent of speed, we need to construct (figuratively) an ideal step motor.

An ideal step motor would have zero mechanical friction, its torque would be

proportional to ampere-turns and its only electrical characteristic would be inductance. Ampere-turns simply mean that torque is proportional to the number of turns of wire in the motor’s stator multiplied by the current passing through those turns of wire.

Anytime there are turns of wire surrounding a magnetic material such as the iron in the motor’s stator, it will have an electrical property called inductance. Inductance describes the energy stored in a magnetic field anytime current passes through this coil of wire. Inductance (L) has a property called inductive reactance, which for the purposes of this discussion may be thought of as a resistance proportional to frequency and therefore motor speed.

According to ohm’s law, current is equal to voltage divided by resistance. In this case we substitute inductive reactance for resistance in ohm’s law and conclude motor current is the inverse of motor speed.

EOC

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Since torque is proportional to ampere-turns (current times the number of turns of wire in the winding), and current is the inverse of speed, torque also has to be the inverse of speed.

In an ideal step motor, as speed approaches zero, its torque would approach infinity while at infinite speed torque would be zero. Because current is proportional to torque, motor current would be infinite at zero speed as well.

Electrically, a real motor differs from an ideal one primarily by having a non-zero winding resistance. Also the iron in the motor is subject to magnetic saturation, as well as having eddy current and hysteresis losses. Magnetic saturation sets a limit on current to torque proportionality while eddy current and hysteresis (iron losses) along with winding resistance (copper losses) cause motor heating.

Motors convert electrical energy into mechanical energy. A stepper motor converts electrical pulses into specific rotational movements. The movement created by each pulse is precise and repeatable, which is why stepper motors are so effective for

positioning applications.

Permanent Magnet stepper motors incorporate a permanent magnet rotor, coil windings and magnetically conductive stators. Energizing a coil winding creates an

electromagnetic field with a north and south pole as shown in figure 1. The stator carries the magnetic field which causes the rotor to align itself with the magnetic field. The magnetic field can be altered by sequentially energizing or “stepping” the stator coils which generates rotary motion.

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Figure 2 illustrates a typical step sequence for a two phase motor. In Step 1 phase A of a two phase stator is energized. This

magnetically locks the rotor in the position shown, since unlike poles attract. When phase A is turned off and phase B is turned on, the rotor rotates 90clockwise. In Step 3, phase B is turned off and phase A is turned on but with the polarity reversed from Step 1. This causes another 90rotation. In Step 4, phase A is turned off and phase B is turned on, with polarity reversed from Step 2. Repeating this sequence causes the rotor to

rotate clockwise in 90steps.

The stepping sequence illustrated in figure 2 is called “one phase on” stepping.

A more common method of stepping is “two phase on” where both phases of the

motor are always energized. However, only the polarity of one phase is switched

at a time, as shown in figure 3. With two phase on stepping the rotor aligns itself

between the “average” north and “average” south magnetic poles. Since both

phases are always on, this method gives 41.4% more torque than “one phase on”

stepping, but with twice the power input.

Half Stepping

The motor can also be “half stepped” by inserting an off state between

transitioning phases. This cuts a stepper’s full step angle in half. For example, a

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90stepping motor would move 45on each half step, figure 4. However, half

stepping typically results in a 15% - 30% loss of torque depending on step rate

when compared to the two phase on stepping sequence. Since one of the windings

is not energized during each alternating half step there is less electromagnetic

force exerted on the rotor resulting in a net loss of torque.

Bipolar Winding

The two phase stepping sequence described utilizes a “bipolar coil winding.”

Each phase consists of a single winding. By reversing the current in the windings,

electromagnetic polarity is reversed. The output stage of a typical two phase bipolar drive is further illustrated in the electrical

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schematic diagram and stepping sequence in figure 5. As illustrated, switching simply reverses the current flow

through the winding thereby changing the polarity of that phase.

Unipolar Winding

Another common winding is the unipolar winding. This consists of two

windings on a pole connected in such a way that when one winding is energized a

magnetic north pole is created, when the other winding is energized a south pole is

created. This is referred to as a unipolar winding because the electrical polarity,

i.e. current flow, from the drive to the coils is never reversed. The stepping sequence is illustrated in figure 6. This design allows for a simpler electronic drive.

However, there is approximately 30% less torque available compared to a bipolar

winding. Torque is lower because the energized coil only utilizes half as much

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Accuracy

The accuracy for can-stack style steppers is 6 - 7% per step, non-cumulative.

A 7.5stepper will be within 0.5of theoretical position for every step, regardless

of how many steps are taken. The incremental errors are non-cumulative because

the mechanical design of the motor dictates a 360movement for each full

revolution. The physical position of the pole plates and magnetic pattern of the

rotor result in a repeatable pattern through every 360rotation (under no load

conditions).

Resonance

Stepper motors have a natural resonant frequency as a result of the motor

being a spring-mass system. When the step rate equals the motor’s natural frequency,

there may be an audible change in noise made by the motor, as well as an

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increase in vibration. The resonant point will vary with the application and load,

but typically occurs somewhere between 70 and 120 steps per second. In severe

cases the motor may lose steps at the resonant frequency. Changing the step rate

is the simplest means of avoiding many problems related to resonance in a system.

Also, half stepping or micro stepping usually reduces resonance problems. When

accelerating to speed, the resonance zone should be passed through as quickly as

possible.

Torque

The torque produced by a specific rotary stepper motor is a function of:

• The step rate

• The current through the windings • The type of drive used

(The force generated by a linear motor is also dependent upon these factors.)

Torque is the sum of the friction torque (Tf) and inertial torque (Ti).

T= T

f

+ T

i

The frictional torque (ounce-inches or gram-cm) is the force (F), in ounces or

grams, required to move a load multiplied by the length, in inches or cm, of the

lever arm used to drive the load (r) as shown in figure 8.

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Figure 8. Frictional torque is the force (F)

required to move a load multiplied by the length of the lever arm (r).

The inertial torque (Ti) is the torque required to accelerate the load (gram-cm2).

It should be noted that as the step rate of a motor is increased, the back electromotive force (EMF) (i.e. the generated voltage) of the motor also increases. This restricts current flow and results in a decrease in useable output torque.

AC Synchronous Motors

Stepping motors can also be run on AC (Alternating Current). However,

one phase must be energized through a properly selected capacitor. In this case

the motor is limited to only one synchronous speed. For instance, if 60 hertz is

being supplied, there are 120 reversals or alterations of the power source. The

phase being energized by a capacitor is also producing the same number of alterations at an offset time sequence. The motor is really being energized at the

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equivalent of 240 steps per second. For a 15rotary motor, 24 steps are required

to make one revolution (24 SPR). This becomes a 600 RPM synchronous motor.

In the case of a linear actuator the linear speed produced is dependent on the

resolution per step of the motor. For example if 60 hertz is supplied to a .001”/

step motor the resulting speed is .240” per second (240 steps per second times

.001”/step). Many of HSI’s stepping motors are available as 300 or 600 RPM

AC synchronous motors.

Drives

Stepper motors require some external electrical components in order to run.

These components typically include a power supply, logic sequencer, switching

components and a clock pulse source to determine the step rate. Many commercially available drives have integrated these

components into a complete package. Some basic drive units have only the final power stage without the controller electronics to generate the proper step sequencing.

Bipolar Drive

This is a very popular drive for a two phase bipolar motor having four leads.

In a complete driver/controller the electronics alternately reverse the current in

each phase. The stepping sequence is shown in figure 5.

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This drive requires a motor with a center-tap at each phase (6 leads). Instead of reversing the current in each phase, the drive only has to switch current from one coil to the other in each phase (figure 6). The windings are such that this switching reverses the magnetic fields within the motor. This option makes for a simpler drive but only half of the copper winding is used at any one time. This results in approximately 30% less available torque in a rotary motor or force in alinear actuator as compared to an equivalent bipolar motor.

L/R Drives

This type of drive is also referred to as a constant voltage drive. Many of

these drives can be configured to run bipolar or unipolar stepper motors. L/R

stands for the electrical relationship of inductance (L) to resistance (R). Motor coil

impedance vs. step rate is determined by these parameters. The L/R drive should

“match” the power supply output voltage to the motor coil voltage rating for continuous duty operation. Most published motor performance curves are based on

full rated voltage applied at the motor leads. Power supply output voltage level

must be set high enough to account for electrical drops within the drive circuitry for optimum continuous operation.

Performance levels of most steppers can be improved by increasing the applied

voltage for shortened duty cycles. This is typically referred to as “over-driving”

the motor. When over-driving a motor, the operating cycle must have sufficient

periodic off time (no power applied) to prevent the motor temperature rise

from exceeding the published specification.

Chopper Drives

A chopper drive allows a stepper motor to maintain greater torque or force

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at higher speeds than with an L/R drive. The chopper drive is a constant current

drive and is almost always the bipolar type. The chopper gets its name from the

technique of rapidly turning the output power on and off (chopping) to control

motor current. For this setup, low impedance motor coils and the maximum voltage power supply that can be used with the drive will deliver the best performance. As a general rule, to achieve optimum performance, the recommended ratio between power supply and rated motor voltage is eight to one. An eight to one ratio was used for the performance curves in this catalog.

Microstepping Drives

Many bipolar drives offer a feature called microstepping. Microstepping

electronically divides a full step into smaller steps. For instance, if one step of a

linear actuator is 0.001 inch, this can be driven to have 10 microsteps per step. In

this case, one microstep would normally be 0.0001 inch. Microstepping effectively

reduces the step increment of a motor. However, the accuracy of each microstep

has a larger percentage of error as compared to the accuracy of a full step. As

with full steps, the incremental errors of microsteps are non-cumulative.

Fatigue / Life

With proper application, HSI’s linear actuators deliver up to 20 million cycles

and HSI’s rotary motors provide up to 25,000 hours of service. Ultimately motor

fatigue and resultant life are determined by each customer’s unique application.

The following definitions are important for understanding motor life

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Continuous Duty: Running a motor at its rated voltage.

25% Duty Cycle: Running a motor at double its rated voltage on an L/R

drive. The motor is “on” approximately 25% of the time. The motor

generates about 60% more output than at rated voltage. Note, duty

cycle is not related to the load placed on the motor.

Life: A linear actuator’s life is the number of cycles that the motor is able to

move at a prescribed load and maintain step accuracy. Rotary motor life

is the number of hours of operation.

One Cycle: A linear actuator’s cycle consists of extending and retracting

back to the original position.

Terminology :

Detent or residual torque: The torque required to rotate the motor’s output

shaft with no current applied to the windings.

Drives: A term depicting the external electrical components to run a Stepper

Motor System. This will include power supplies, logic sequencers, switching components and usually a variable frequency pulse source to determine the step rate.

Dynamic torque: The torque generated by the motor at a given step rate. Dynamic

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Holding torque: The torque required to rotate the motor’s output shaft while the

windings are energized with a steady state D.C. current.

Inertia: The measure of a body’s resistance to acceleration or deceleration.

Typically used in reference to the inertia of the load to be moved by a motor or the

inertia of a motor’s rotor.

Linear step increment: The linear travel movement generated by the leadscrew

with each single step of the rotor.

Maximum temperature rise: Determined by the resistance rise method, motor

unmounted in free air and energized with a steady state D.C. current.

Pull in torque: The load a motor can move without missing steps when started

at a constant pulse rate.

Pull out torque: The load a motor can move when at operating speed. This is

normally substantially greater than the Pull in torque.

Pulse rate: The number of pulses per second (pps) applied to the windings of the

motor. The pulse rate is equivalent to the motor step rate. Pulses per second (PPS): The number of steps that the motor takes in one

second (sometimes called “steps per second”). This is determined by the frequency

(35)

Ramping: A drive technique to accelerate a given load from a low step rate, to a

given maximum step rate and then to decelerate to the initial step rate without the